Oxygen barrier oriented film

ABSTRACT

A coextruded multiple layer oriented film comprises a core layer of a blend of ethylene vinyl alcohol copolymer and polyamide, two intermediate adhesive layers, and two outer layers of a blend of linear low density polyethylene, linear medium density polyethylene, and ethylene vinyl acetate copolymer. A preferred embodiment of the multilayer film exhibits excellent optics and shrink properties while providing high oxygen barrier especially useful in food packaging applications.

BACKGROUND OF THE INVENTION

This invention relates to oriented thermoplastic films for packaging;and more particularly, this invention relates to a coextruded,multilayer, oriented film having high oxygen barrier characteristics.

Thermoplastic film, and in particular polyolefin materials, have beenused for some time in connection with packaging of various articlesincluding food products which require protection from the environment,an attractive appearance, and resistance to abuse during the storage anddistribution cycle. Suitable optical properties are also desirable inorder to provide for inspection of the packaged product after packaging,in the distribution chain, and ultimately at point of sale. Opticalproperties such as high gloss, high clarity, and low hazecharacteristics contribute to an aesthetically attractive packagingmaterial and packaged product to enhance the consumer appeal of theproduct. Various polymeric materials have been used to provide lower gaspermeability in order to reduce the transmission of oxygen through thepackaging film and thereby retard the spoilage and extend the shelf lifeof products such as food items which are sensitive to oxygen.

It is also desirable to include in a packaging film a shrink feature,i.e., the propensity of the film upon exposure to heat to shrink or, ifrestrained, create shrink tension within the packaging film. Thisproperty is imparted to the film by orientation of the film during itsmanufacture. Typically, the manufactured film is stretched in either alongitudinal (machine) direction, a transverse direction, or both, invarying degrees to impart a certain degree of shrinkability in the filmupon subsequent heating. After being so stretched, the film is rapidlycooled to provide this latent shrinkability to the resulting film. Oneadvantage of shrinkable film is the tight, smooth appearance of thewrapped product that results, providing an aesthetic package as well asprotecting the packaged product from environmental abuse. Various foodand non-food items may be and have been packaged in shrinkable films.

It is sometimes also desirable to orient the packaging film andthereafter heat set the film by bringing the film to a temperature nearits orientation temperature. This produces a film with substantiallyless shrinkability, while retaining much of the advantages oforientation, including improved modulus and optical properties.

Ethylene vinyl alcohol copolymer (EVOH) is known as an oxygen barriermaterial and has been used in the past in conjunction with multilayerpackaging films. EVOH also provides a good barrier to odors orfragrances. Orienting EVOH to produce a heat shrinkable film has provento be difficult. During the stretching or racking step for orientingsuch a film, the EVOH can sometimes develop voids. This phenomenon canresult in some loss of oxygen barrier properties, which can affect, i.e.reduce the effective shelf life of food products packaged in EVOH film.

The presence of voids in the EVOH layer can also result in discolorationof a food product, such as processed meat, and therefore reduce theappearance and market value of a packaged food item.

U.S. Pat. No. 4,064,296 issued to Bornstein et al discloses a filmformed by the coextrusion of hydrolyzed vinyl acetate (HEVA) withoutside layers of, for example, ethylene vinyl acetate copolymer (EVA).

Also of interest is U.S. Pat. No. 4,464,443 issued to Farrell et alshowing the use of EVOH in a multilayer polymer structure, and includingdrying agents or desiccants such as sodium phosphate-di-basic andcalcium chloride. EVOH, although a good barrier material, is moisturesensitive, and loses a great deal of its barrier properties at higherlevels of relative humidity.

Also of interest is U.S. Pat. No. 4,457,960 issued to Newsome whichdiscloses the use of EVOH and EVOH blends in a multiple layer film. Thefilm may be made as shrinkable film, and may be melt extruded. Theoutside layer of the multiple layer film may be a blend of linear lowdensity polyethylene (LLDPE) and EVA.

Also of interest is U.S. Pat. No. 4,495,249 issued to Ohya et al anddisclosing a multilayer laminate film with a core layer of a saponifiedcopolymer of ethylene and vinyl acetate, and including two outer layersof a mixture of EVA and LLDPE. The multilayer laminate film of thisreference can be made heat shrinkable and has gas barrier properties.

U.S. Pat. No. 4,501,797 issued to Super et al discloses an unbalancedoriented multiple layer film including an intermediate layer ofanhydride modified polypropylene and a barrier layer of a blend ofethylene vinyl alcohol and nylon.

U.S. Pat. No. 4,501,798 issued to Koschak et al also discloses the useof a blend of EVOH and nylon and an unbalanced multiple layer polymericfilm also including LLDPE or EVA in a sealant layer. Adhesive layers ofmaterials having carboxy moieties and preferably anhydride derivativesare present. The film of the reference is characterized by having highbarrier to gaseous transmission, high gloss, transparency and stiffness.

U.S. Pat. No. 4,347,332 issued to Odorzynski et al discloses a filmhaving a blend of nylon and ethylene vinyl alcohol copolymer.

U.S. Pat. No. 4,514,465 issued to Schoenberg discloses a five layeredthermoplastic film, oriented and irradiated, having a three componentblend of LLDPE, LMDPE, and EVA, and a four component surface layerhaving LLDPE, LMDPE, and EVA combined with a UV stabilizer.

Copending U.S. application Ser. No. 694,362, assigned to a commonassignee with the present application, discloses a five-layerthermoplastic film having two cross-linked surface layers ofLLDPE/LMDPE/EVA.

It is an object of the present invention to provide a coextrudedthermoplastic multilayer film characterized by good oxygen barrierproperties over a wide range of moisture conditions.

It is also an object of the present invention to provide a coextrudedthermoplastic multilayer film which is substantially free of voids inthe barrier material of the film.

It is a further object of the present invention to provide athermoplastic multilayer film having an aesthetic appearance with goodclarity, and other desirable optical properties.

It is another object of the present invention to provide a thinthermoplastic multilayer film having superior toughness and abrasionresistance.

It is still another object of the present invention to provide acoextruded thermoplastic multilayer film which may be totallycoextruded, and oriented to provide a film with good shrink propertiesand good barrier properties over a wide range of moisture conditions.

It is a yet another object of the present invention to provide acoextruded thermoplastic film which is oriented yet substantially shrinkfree.

SUMMARY OF THE INVENTION

The present invention relates to an oriented multilayer film comprisinga cross-linked core layer comprising a blend of an ethylene vinylalcohol copolymer and a polyamide resin; two cross-linked interiorlayers each comprising an adhesive resin; and two cross-linked surfacelayers each comprising a three component blend of a linear low densitypolyethylene, a linear medium polyethylene, and an ethylene vinylacetate copolymer.

In another aspect of the invention, a method of making an orientedmultilayer film comprises the steps of simultaneously coextruding a corelayer of a blend of an ethylene vinyl alcohol copolymer and a polyamideresin, two intermediate layers of an adhesive material, and two outerlayers of a blend of a linear low density polyethylene, a linear mediumdensity polyethylene, and an ethylene vinyl acetate copolymer; rapidlycooling the coextruded film; collapsing the cooled film; heating thecollapsed film to a temperature between about 105° C. and 115° C.; andstretching and orienting the heated film.

DEFINITIONS

"Intermediate layer", "interior layer", and the like is used herein todefine a layer in a multilayer film enclosed on both sides by otherlayers.

The term "oriented" and the like is used herein to define a polymericmaterial in which the molecules have been aligned by a process such asracking or blown bubble process.

The term "ethylene vinyl alcohol copolymer", "EVOH", and the like isused herein to include saponified or hydrolyzed ethylene vinyl acetatecopolymers.

The term "racking" is used herein to define a well-known process forstretching coextruded and reheated multilayer film by means of tenterframing or blown bubble processes.

The term "linear low density polyethylene", "LLDPE", and the like areused herein to refer to copolymers of ethylene with one or morecomonomers selected from C₄ to C₁₀ alpha oleofins such as butene-1,octene, etc. in which the molecules of the copolymers comprise longchains with few side chain branches or cross-linked structures. Thismolecular structure is to be contrasted with conventional low or mediumdensity polyethylenes which are more highly branched than theirrespective counterparts.

"LLDPE" as defined herein has a density usually in the range of fromabout 0.916 grams per cubic centimeter to about 0.925 grams per cubiccentimeter.

The terms "linear medium density polyethylene", "LMDPE" and the like asused herein refers to copolymers as described above and having a densityusually in a range of from about 0.926 grams per cubic centimeter toabout 0.941 grams per cubic centimeter.

The terms "ethylene vinyl acetate copolymer", "EVA" and the like is usedherein to refer to a copolymer formed from ethylene and vinyl acetatemonomers wherein the ethylene derived units in the copolymer are presentin major amounts, preferably between about 60% and 98% by weight, andthe vinyl acetate derived units in the copolymer are present in minoramounts, preferably between about 2% and 40% by weight.

The term "oriented" and the like is used herein to define a materialwhich, when heated to an appropriate temperature above room temperature(for example 96° C.), will have free shrink of 5% or greater in at leastone linear direction.

All compositional percentages used herein are calculated on a "byweight" basis.

The term "polyamide" and the like refers to high molecular weightpolymers having amide linkages along the molecular chain, and refersmore specifically to synthetic polyamide such as various nylons.

BRIEF DESCRIPTIONS OF THE DRAWINGS

Further details are given below with reference to the sole drawingFIGURE where FIG. 1 is a schematic cross-section of a preferredembodiment of a multilayer film of the invention.

DESCRIPTIONS OF THE PREFERRED EMBODIMENTS

Referring specifically to the drawings, in FIG. 1, a schematiccross-section of the preferred embodiment of the coextruded multilayeroriented film of the invention is shown. Film structure is directed to amultilayer film having the generalized structure of A/B/C/B/A where A isan outer layer, B is an intermediate adhesive layer, and C is a corelayer containing a blend of a barrier material and a polyamide.Preferably, the outer layers A each comprise about 35% of the totalmultilayer film thickness; the intermediate layers B each comprise about10% of the film thickness, and the barrier/polyamide layer C about 10%of the total film thickness. The total thickness of the multilayer filmis preferably between about 0.5 and 2.0 mils, and more preferablybetween 0.75 and 1.5 mils. Even more preferably, the multilayer film ofthe present invention is about 1 mil thick.

Preferably, core layer 10 is a blend of ethylene vinyl alcohol copolymerand a polyamide or copolymer comprising polyamide comonomers. Core layer10 preferably forms between about 5% and 25% of the total filmthickness. Thicknesses less than about 5% result in a very thin filmwith possible voids in the barrier material. Thicknesses greater thanabout 25% make the film difficult to stretch or rack, and also result inincreased cost due to the expensive barrier component.

Intermediate layers 12 and 14 are preferably acid or acidanhydride-modified polymeric material which can bond the core layer 10to the outer layers 16 and 18. This material preferably includes a graftcopolymer of a polyolefin, such as polyethylene, or ethylene-estercopolymer substrate and an unsaturated carboxylic acid or acidanhydride, blended with a polyolefin, such as polyethylene, orethylene-ester copolymer.

Outer layers 16 and 18 are preferably a three component blend of LLDPE,LMDPE, and EVA. These outer layers preferably include from about 40% toabout 60% by weight of LLDPE, from about 20% to about 30% by weight ofLMDPE, and from about 20% to about 30% by weight of EVA. Morepreferably, the outer layers 16 and 18 include about 50%, by weight, ofa LLDPE, about 25%, by weight, of LMDPE, and about 25%, by weight, ofEVA.

The EVA has a vinyl acetate (VA) content of preferably between about 3.5and 9% by weight and more preferably between about 3.5 and 5% by weight.At VA contents greater than about 9%, the multilayer film becomes toosticky or tacky for many applications, or requires the use of relativelylarge amounts of slip and anit-block additives.

The film is preferably irradiated with between about 3 and 13 megarads(M.R.) of irradiation, even more preferably between about 5 and 10 M.R.,prior to orientation of the film. Orientation is done by racking orstretching the film at a racking ratio of from between about 3.0 andabout 5.0 times the original dimensions of the film in the longitudinal(machine) and transverse directions.

EXAMPLE 1

A sample film was prepared by blending 50% of LLDPE (Dowlex 2045), 25%LMDPE (Dowlex 2037) and 15% EVA having a vinyl acetate of about 3.6%,blended with about 10% of a masterbatch concentrate containing slip andantiblock additives compounded with EVA of about 31/2% vinyl acetatecontent by weight. This outside blend layer was coextruded with a corelayer containing a blend of 90% EVOH (EVAL H) and 10% of a nylon 6/nylon12 copolymer (Grillon CA-6), and an intermediate adhesive (NorchemPlexar 3150).

The Dowlex 2045 may be obtained from Dow Chemical Company. This is anespecially preferred LLDPE for use in this invention, and is a copolymerof ethylene and octene and has a density of 23° C. of about 0.920 gramsper cubic centimeter and a melt flow index of from about 0.7 to about1.2 grams per ten minutes (as measured by ASTM-D-1238, E-28). LLDPE addstoughness to the film.

A preferred LMDPE is Dowlex 2037, also obtainable from Dow ChemicalCompany. This resin is a copolymer of ethylene and octene and has adensity at 23° C. of about 0.935 grams per cubic centimeter and a meltflow index of about 2.55 grams per ten minutes (ASTM-D-1238, E-28). TheLMDPE imparts stiffness, i.e. high modulus, to the film withoutsignificantly sacrificing toughness. The high modulus characteristic ofthe film is especially desirable in form-fill-seal applications wherethe film is fed as a lay-flat film and then formed on a forming shoeinto a tube.

The EVA of the outside blend layer is commercially available from ElPaso Polyolefins Company under the trade designation El Paso PE204-CS95. This material has a density at 23° C. of from about 0.9232 toabout 0.9250 grams per cubic centimeter and a melt flow (ASTM-D-1238,E-28) of about 2.0±0.5 grams per ten (10) minutes. The vinyl acetatecontent of this EVA is about 3.6% by weight.

EVA improves the processability of the film, and also provides a sealinglayer which can be adequately sealed at relatively low temperatures, orelse provides a stronger seal at a given temperature, than many otherpolymeric resins.

The EVOH of the core blend layer was EVAL H, available from EVAL Companyof America and having the ethylene content of about 38% by weight and amelt index of about 1.5 grams/10 minutes. Other suitable EVOH resinsinclude EVAL E, EVAL F, and EVAL K, as well as blends of the above, andpreferably such resins or blends having a melt index of between about 1to 4 grams per ten minutes (ASTM 1238). Grillon CA-6, available fromEmser Industries, was blended with the EVOH. The Grillon CA-6 is a nyloncopolymer having about 60% nylon 6 and about 40% nylon 12 by weight.

Although nylon 12 would be effective alone as a blending material in thecore layer, this is a relatively expensive material. Nylon 6 alone wouldbe effective as a blending material, but with some difficulty inprocessing. The particular blend employed proved to be very advantageousin providing an economical yet effective means for providing a coreblend having the good barrier properties associated with EVOH, but withthe processing and elongation advantages of nylon. Another suitablenylon copolymer is Grillon CR-9, having 20-30% nylon 6 and 70-80% nylon12 by weight.

The intermediate adhesive material, Norchem Plexar 3150, is a lowdensity polyethylene-based anhydride-modified resin produced by Norchem.Other anhydride-modified adhesives such as CXA-162 (duPont) can also beused as the intermediate adhesive.

The polymer belt from the coextrusion die was then cooled and cast intoa solid tape which was irradiated with about 8 megarads of irradiation.The tape was then heated to about 110° C. in an oven and blown into abubble. The bubble was expanded to about 3.5 times its originaldimensions in both the machine (longitudinal) and transverse directions,and then deflated and ply separated into single wound film rolls. Thefinal film had a thickness of about one mil, and in addition to theshrink properties imparted by orientation, exhibited excellenttoughness, good optics, burn out resistance, resistance to tearpropagation, and heat sealability. The film also exhibited good abuseresistance and the necessary stiffness and lower tack required forpackaging applications and was substantially free of voids in theEVOH/polyamide blend layer.

Test results for the sample film are listed below in Table I.

                  TABLE I                                                         ______________________________________                                        Tensile at Break and 73° F. (PSI).sup.1                                Avg..sup.2 Longitudinal                                                                             1151.0 × 100                                      Std. Dev              82.3 × 100                                        95% C.L..sup.3        130.9 × 100                                       Avg. Transverse       887.5 × 100                                       Std. Dev.             25.4 × 100                                        95% C.L.              40.4 × 100                                        Elongation at Break and 73° F. (%).sup.4                               Avg. Longitudinal     86.                                                     Std. Dev.             6.                                                      95% C.L.              9.                                                      Avg. Transverse       151.                                                    Std. Dev.             21.                                                     95% C.L.              33.                                                     Modulus at 73° F. (PSI).sup.5                                          Avg. Longitudinal     89.7 × 1000                                       Std. Dev.              3.2 × 1000                                       95% C.L.               5.2 × 1000                                       Avg. Transverse       81.6 × 1000                                       Std. Dev.              4.5 × 1000                                       95% C.L.               7.2 × 1000                                       Tear Propagation                                                              at 73° F. (grams).sup.6                                                Avg. Longitudinal     13.44                                                   Std. Dev.             1.45                                                    95% C.L.              2.31                                                    Avg. Transverse       19.25                                                   Std. Dev.             3.30                                                    95% C.L.              5.26                                                    Free Shrink (%) at 220° F..sup.7                                       Avg. Longitudinal     22.                                                     Std. Dev.             1.                                                      95% C.L.              2.                                                      Avg. Transverse       33.                                                     Std. Dev.             1.                                                      95% C.L.              1.                                                      Free Shrink at 240° F.                                                 Avg. Longitudinal     66.                                                     Std. Dev.             1.                                                      95% C.L.              1.                                                      Avg. Transverse       64.                                                     Std. Dev.             1.                                                      95% C.L.              2.                                                      Free Shrink at 260° F.                                                 Avg. Longitudinal     69.                                                     Std. Dev.             0.                                                      95% C.L.              0.                                                      Avg. Long.            64.                                                     Std. Dev.             1.                                                      95% C.L.              1.                                                      Shrink Properties at 220° F.                                           Shrink Force (lbs).sup.8                                                      Avg. Longitudinal     0.439                                                   Std. Dev.             0.013                                                   95% C.L.              0.021                                                   Avg. Transverse       0.533                                                   Std. Dev.             0.015                                                   95% C.L.              0.024                                                   Shrink Tension (PSI).sup.9                                                    Avg. Longitudinal     374.                                                    Std. Dev.             22.                                                     95% C.L.              35.                                                     Avg. Transverse       434.                                                    Std. Dev.             15.                                                     95% C.L.              23.                                                     Shrink Properties at 240° F.                                           Shrink Force (lbs.)                                                           Avg. Longitudinal     0.459                                                   Std. Dev.             0.013                                                   95% C.L.              0.021                                                   Avg. Transverse       0.500                                                   Std. Dev.             0.014                                                   95% C.L.              0.022                                                   Shrink Tension (PSI)                                                          Avg. Longitudinal     389.                                                    Std. Dev.             11.                                                     95% C.L.              18.                                                     Avg. Transverse       414.                                                    Std. Dev.             14.                                                     95% C.L.              22.                                                     Shrink Properties at 260° F.                                           Shrink Force (lbs)                                                            Avg. Longitudinal     0.383                                                   Std. Dev.             0.034                                                   95% C.L.              0.054                                                   Avg. Transverse       0.509                                                   Std. Dev.             0.037                                                   95% C.L.              0.059                                                   Shrink Tension (PSI)                                                          Avg. Longitudinal     338.                                                    Std. Dev.             31.                                                     95% C.L.              49.                                                     Avg. Transverse       457.                                                    Std. Dev.             29.                                                     95% C.L.              46.                                                     Optical Properties at 73° F.                                            Haze (%).sup.10                                                              Avg.                  2.9                                                     Std. Dev.             0.2                                                     95% C.L.              0.4                                                     Clarity (%).sup.11                                                            Avg.                  65.2                                                    Std. Dev.             3.6                                                     95% C.L.              5.7                                                     Gloss (45°).sup.12                                                     Avg.                  84.                                                     Std. Dev.             2.                                                      95% C.L.              4.                                                      Oxygen Transmission                                                           at 73° F., 0% RH.sup.13                                                Sample 1              7.3                                                     Sample 2              7.6                                                     Sample 3              7.8                                                     ______________________________________                                         The following footnotes apply to Table I.                                     .sup.1 ASTM D88281.                                                           .sup.2 All values in Table I are averages obtained from four (4) replicat     measurements.                                                                 .sup.3 C.L. is Confidence Limit  e.g., if the reported average value was      10 and the 95% C.L. was 2, then if one hundred replicate readings were        made, 95 of them would have a value between 8 and 12, inclusive.              .sup.4 ASTM D882-81.                                                          .sup.5 ASTM D882-81.                                                          .sup.6 ASTM D1938-79.                                                         .sup.7 ASTM D2732-70 (reapproved 1976).                                       .sup.8 ASTM D2838-81 (shrink free = shrink tension × film thickness     in mils × 1000)                                                         .sup.9 ASTM D2838-81                                                          .sup.10 ASTM D1003-61 (reapproved 1977)                                       .sup.11 ASTM D1746-70                                                         .sup.12 ASTM D2457-70 (reapproved 1977)                                  

EXAMPLE 2

A sample film was prepared according to the same procedure andformulation described in Example 1, having Plexar 158 as an intermediateadhesive layer, but without a polyamide in the core layer. This filmexhibited voids in the EVOH layer. Processed meat (bologna) packaged inthe film was found to discolor at regions adjacent the void areas of theEVOH core layer.

Obvious modifications to the invention as described may be made by oneskilled in the art without departing from the spirit and scope of theclaims as presented below.

What is claimed is:
 1. An oriented multilayer film comprising:(a) across-linked core layer comprising a blend of an ethylene vinyl alcoholcopolymer and a polyamide resin, said blend forming between about 5% and25% of the total film thickness; (b) two cross-linked interior layerseach comprising an adhesive resin; (c) two cross-linked outer layerseach comprising a three-component blend of a linear low densitypolyethylene, a linear medium density polyethylene, and an ethylenevinyl acetate copolymer; and (d) said film having a total thicknessranging from about 0.75 to 1.5 mils.
 2. An oriented five-layer filmcomprising:(a) a cross-linked core layer comprising a blend of (1) fromabout 80%, by weight, to about 99%, by weight, of an ethylene vinylalcohol copolymer and (2) from about 1%, by weight, to about 20%, byweight of a polyamide resin, said blend forming between about 5% and 25%of the total film thickness; (b) two cross-linked interior layers eachcomprising an adhesive resin; (c) two cross-linked surface layers eachcomprising a blend of (1) from about 40%, by weight, to about 60%, byweight, of a linear low density polyethylene, (2) from about 20%, byweight, to about 30%, by weight of a linear medium density polyethylene,and (3) from about 20%, by weight, to about 30%, by weight, of anethylene vinyl acetate copolymer; and (d) said film having a totalthickness ranging from about 0.75 to 1.5 mils.
 3. An oriented five-layerfilm comprising:(a) a cross-linked core layer comprising a blend of (1)about 90%, by weight, of an ethylene vinyl alcohol copolymer, and (2)about 10%, by weight, of a polyamide resin, said blend forming betweenabout 5% and 25% of the total film thickness; (b) two cross-linkedinterior layers each comprising an acid or acid anhydride-modifiedpolymeric material; (c) two cross-linked surface layers each comprisinga blend of (1) about 50% by weight, of a linear low densitypolyethylene, (2) about 25%, by weight, of a linear medium densitypolyethylene and (3) about 25%, by weight, of an ethylene vinyl acetatecopolymer; and (d) said film having a total thickness ranging from about0.75 to 1.5 mils.
 4. The film of claims 1, 2 or 3 wherein said ethylenevinyl acetate copolymer comprises from about 3.5%, by weight, to about9%, by weight, of vinyl acetate derived units.
 5. The film of claims 1,2, or 3 wherein said ethylene vinyl acetate copolymer comprises fromabout 3.5%, by weight, to about 5%, by weight, of vinyl acetate derivedunits.
 6. The film of claims 1, 2, or 3 wherein said ethylene vinylacetate copolymer comprises from about 3.6%, by weight, of vinyl acetatederived units.
 7. The film of claims 1, 2 or 3 which has beencross-linked with from about three megarads to about thirteen megaradsof irradiation.
 8. The film of claims 1, 2 or 3 which has beencross-linked with from about five megarads to about ten megarads ofirradiation.
 9. The film of claims 1, 2 or 3 which has been cross-linkedwith about eight megarads of irradiation.
 10. The film of claims 1, 2 or3 which has been oriented by racking at a racking ratio of from about3.0 to about 5.0 in both the longitudinal and transverse directions. 11.The film of claims 1, 2 or 3 which has been oriented by racking at aracking ratio of about 3.5 in both the longitudinal and transversedirections.
 12. A method of making an oriented multilayer barrier filmhaving a total thickness ranging from about 0.75 to 1.5 milscomprising:(a) simultaneously coextruding a core layer of a blend of anethylene vinyl alcohol copolymer and a polyamide resin, two intermediatelayers of an adhesive material, and two outer layers of a blend of alinear low density polyethylene, a linear medium density polyethylene,and an ethylene vinyl acetate copolymer; (b) rapidly cooling thecoextruded film; (c) collapsing the cooled film; (d) irradiating thecooled film with between about 3 and 13 megarads of irradiation; (e)heating the irradiated film to a temperature between about 105° C. and115° C.; and (f) stretching and orienting the heated film.
 13. Themethod of claim 12 wherein the coextruded film is cooled to about roomtemperature.
 14. The method according to claim 12 wherein the heatedfilm is oriented by racking at a racking ratio of from about 3.0 toabout 5.0 in both the longitudinal and transverse directions.
 15. Themethod according to claim 12 wherein the heated film is oriented byracking at a racking ratio of about 3.5 in both longitudinal andtransverse directions.
 16. The method according to claim 12 furthercomprising the step of reheating the oriented film to a temperature nearits orientation temperature to provide a substantially non-shrinkablefilm.